1. Field of the Embodiments
The embodiments described herein are generally directed to components incorporating molybdenum disulfide (MoS2).
2. Description of the Related Art
MoS2 is a semiconductor made of layers that are weakly coupled by van der Waals forces and can be easily separated via chemical or mechanical exfoliation to obtain few-layer or single-layer samples. A layer is made of three atomic planes that are strongly bonded to each other: two hexagonal planes of sulfur atoms separated by one hexagonal plane of molybdenum atoms, with each molybdenum atom covalently bonded to six sulfur atoms in the adjacent planes (see FIG. 1a Layered structure of MoS2, where X represents a S atom and T a Mo atom). Additional description may be found in A. Kuc et al., Influence of quantum confinement on the electronic structure of the transition metal sulfide TS(2), Physical Review B, 83 (2011) which is incorporated herein by reference. FIG. 1b illustrates the effect of quantum confinement on the band structure of MoS2.
Bulk MoS2 is a semiconductor with an indirect bandgap of 1.2 eV. When the thickness is reduced to a few layers, the indirect bandgap is tuned by quantum confinement and increases by 0.5 eV or more, until it eventually exceeds the energy spacing of the direct gap for single-layer thickness, at about 1.9 eV. When varying the thickness, photoluminescence experiments have shown that the quantum yield increases by a few orders of magnitude for single-layer samples, confirming the crossover from indirect to direct gap. For a single layer, the quantum yield has also been found to be higher when the layer is suspended.
These results make single-layer MoS2 a possible candidate for optoelectronics applications, as well as for other device applications where a large energy gap, a large surface area, and a high surface-to-volume ratio are crucial. Presently, the technological potential of this material still remains largely unexplored. Single-layer and few-layer transistors have been only recently realized by depositing thin flakes of MoS2 on a doped silicon substrate capped with an insulating silicon dioxide layer. The MoS2 thin flakes are first deposited using the same method that yielded the first successful single-layer graphene devices, i.e. mechanical exfoliation with scotch tape, then attachment of gold source and drain electrodes across the MoS2 layer. The number of layers can be roughly sorted by contrast imaging with an optical microscope, whereas accurate measurements are obtained either by Raman spectroscopy or by AFM measurements of the thickness, which is about 0.65 nm for a single layer. In some devices, top gates with a different material for gate dielectric are also deposited (see FIG. 2a). Electrical characterization of the device is shown in FIG. 2b. The performance of MoS2 devices has been found to vary greatly depending on the gate dielectric material. For example, HfO2 gate oxide on single layer flakes yielded on-off current ratio as high as 1×108 and mobility higher than 200 cm2V−1 s−1 at room temperature. These first results show that transistors can be obtained.
There is a need in the art to advantageously implement MoS2 in various processes and devices to improvements in light emitting devices, photoelectric devices, superconductivity and the like.